The primary objectives of the proposed research are to devise a chemical method to determine the three-dimensional structure of the nucleoside triphosphate sites of proteins and to apply this approach mainly to the ATPase sites of myosin. The aim would be to synthesize a series of substrate analogs (affinity labels), each of which is capable of specifically labelling (forming a covalent bond with) an amino acid residue of the active site. Peptides containing these tagged residues would then be isolated and their sequences determined. Knowing these sequences and the proximity of the tagged residues to the substrate would permit the formulation of a three-dimensional map of the site. Identification of the residues near the triphosphate portion of the binding site would be particularly valuable in defining the mechanism of ATP hydrolysis and hence of the central feature of contractile systems, chemical-to-mechanical energy transduction. Another feature of the contractile apparatus is protein-protein interaction. As an extension of studies previously carried out on actin, the nature of the interactions between myosin and actin, tropomyosin and actin, and so on, would be examined, using mainly the conformation-sensitive technique of circular dichroism. These studies would be aided in part by the use of environmentally sensitive substrate analogs, which would, when protein-bound, monitor interaction-dependent changes.